In a digital communication system, due to multipath fading caused by transmission signals reflected by buildings or the like, and Doppler fluctuations caused by movement of a terminal, frequency selective fading and fluctuations of transmission delay time occur in transmission channels. Under such multipath environments, a received signal is a resultant signal of a transmission signal interfered with signals arrived after delay times have elapsed.
Regarding such transmission channels with frequency selectivity, a single carrier block transmission system has attracted attentions in recent years (for example, refer to Non-patent document 1 below). With the single carrier (hereinafter, referred to as an SC (Single Carrier)) block transmission system, transmission peak power can be reduced more than with an OFDM (Orthogonal Frequency Division Multiplexing) transmission system that is a type of a multi carrier (hereinafter, referred to as an MC (Multiple Carrier)) block transmission system.
In the SC block transmission, countermeasures against the multipath fading are taken such as a cyclic prefix (hereinafter, referred to as CP (Cyclic Prefix)) insertion that duplicates a rear part of a time domain signal and add it to the beginning of the signal, and a ZP (zero padding) that inserts zeros at the beginning or end part of data. In such a way, in the SC block transmission, transmission peak power can be suppressed while influence of the multipath fading being reduced.
In a general communication system, a spectrum mask indicating the upper limit of spectra outside of an allocated frequency band is determined. In such a communication system, the out-of-band spectra need to be reduced so as to satisfy the spectrum mask. The out-of-band spectra need to be reduced also because they interfere with adjacent channels. However, in the SC block transmission, the out-of-band spectra are generated due to phase discontinuity between SC blocks.
Non-patent document 2 discloses a technique of reducing the out-of-band spectra in which a fixed symbol is inserted in each SC block to maintain continuity of phases between blocks.